1. Field of Disclosure
This invention relates to barriers for protecting shorelines from floodwaters, especially floodwaters prone to wave action.
2. Background
Floodwaters are a major source of property damage. Floodwaters may come from a rising body of water, such as a hurricane driven storm surge, from swollen rivers rising above flood stage from snow melt or heavy rains, or from waters accumulating and rising at ground surface due to sustained rains overwhelming drainage systems. Improved coastal, tidal and riverine areas often employ a shoreline water barrier such as a bulkhead, seawall, dike or levee, to prevent destruction of water front properties by flooding from rising water. Buildings on the shore of a place for a body of water are especially vulnerable to wind driven floodwaters overtopping water barriers.
Steel or concrete walls permanently installed atop water barriers, offer a potential solution for prevent rising water and wind driven waves from overtopping water barriers and damaging or destroying waterfront properties. However, permanent walls along a shoreline tall enough to block overtopping waters and withstand pounding wave action may obscure the view of the waterscape, mar the landscape of often beautiful coastline and riverine areas, and impede recreational use of beaches and shorelines.
Solutions that do not permanently block the view of the waterscape of the place for a body of water lined by the bulkhead, seawall, levee, dike or other shoreline water barrier construction have been proposed. For example, see U.S. Pat. No. 6,338,594 (vertically elevating buoyant walls from an underground chamber into which water is pumped to float the walls upwardly); U.S. Pat. Nos. 5,725,326 and 7,744,310 (use of rising storm waters to fill underground chambers and buoy walls vertically upwardly atop a dike or bulkhead); U.S. Pat. No. 7,033,122 (folded metal wall situated in an accommodation space in a dike that can be unfolded and locked in place by workers). However, these solutions depend upon an available workforce or power to run pumps or upon underground structures susceptible to fouling from accretion of surface materials. Natural riverbanks (that is, not bulkheaded) that are lined by self-elevating stanchions interconnected by sheeting are described in U.S. Pat. No. 4,377,352. The inventor of possible embodiments of the invention described herein has disclosed in U.S. Pat. No. 6,623,209 a system by which doors and other grade level openings are guarded from entrance of water by water buoyant rigid flood barrier panels that are self-actuating.
Aluminum alloys are suitable for use as rigid panels for a self-actuating water buoyant flood barrier, especially in a marine environment, for they are relatively lightweight, corrosion resistant, readily available, and cost effective, and are a material of choice where the self-actuating gate must be load bearing for vehicular or pedestrian traffic. A risen panel of a self-actuating water buoyant flood barrier is held upright by hydrostatic pressure of risen water pressing against it, and is subject to flexural stress, that is, stress normal to the plane of the panel, which tends to bend the panel toward the center of the panel. Rising levels of water steadily and increasingly stress the panel from hydrostatic pressure acting on it. Creeping rises of water levels present little problem of durability for a well-engineered aluminum alloy. A structural limitation of aluminum alloys is, however, their fatigue strength and fatigue limit. Fatigue strength is the stress at which failure occurs for a given number of cycles. Fatigue limit is the load ceiling below which a material will not fail, regardless of the number of cycles of load below that ceiling it is subjected to. Aluminum alloys have no well-defined fatigue limit, meaning that fatigue failure eventually occurs after many cycles, depending on the grade of alloy, even under very small cyclic loadings. However, floodwater storm waves intermittently arriving and crashing onto the panel on top of a risen water level suddenly and cyclically impart massively large loads on a risen panel, steeply increasing stress of the panel more intensely than the comparatively steady force applied from the more slowly changing level of rising or falling water. Cycling pressure spikes from storm waves repetitively crashing onto a rigid aluminum panel over time and from storm to storm hasten the possibility of eventual fatigue and failure of an aluminum alloy panel and other like rigid panels formed of a material suitable for use as a self-actuating water buoyant flood barrier, especially in a corrosive marine environment. This necessitates repair or replacement of the flood barrier. An improvement in this situation is desirable.